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Firefox can't find javascript files on localhost


I'm running firefox 21.0 on windows 8. I've installed Apache 2.4 (64 bit) as a web server on localhost.

I'm getting sporadic unexpected results testing my web pages. When I look at the source code (Ctrl-U) and click on the link to the javaScript files, for some of the files I get the firefox warning page (with exclamation mark in yellow triangle - not the 404 message) claiming that firefox cannot find the javaScript file. The files do exist and capitalization is correct.

The links are coded like this: <script type="text/javascript" src="/cradur/JSLib/dataGrid.js" charset="utf-8"></script> The web page is xhtml1-strict.

IMPORTANT: THIS ERROR IS ONLY OCCURRING SPORADICALLY. The web page (and JS file) will work fine for a time, then suddenly firefox will no longer be able to find the file.

Please note also that the current set up is on a new laptop, which I've only been using for a week. I've previously run firefox/ajax on windows XP for years without encountering this problem.

Additional System Details

Installed Plug-ins

  • Shockwave Flash 11.7 r700
  • Intel web components for Intel® Identity Protection Technology
  • Intel web components updater - Installs and updates the Intel web components
  • Adobe PDF Plug-In For Firefox and Netscape 10.1.3
  • 5.0.61118.0


  • Firefox 21.0
  • User Agent: Mozilla/5.0 (Windows NT 6.2; WOW64; rv:21.0) Gecko/20100101 Firefox/21.0
  • Support URL: http://support.mozilla.org/1/firefox/21.0/WINNT/cy/


  • Firebug 1.11.4 (firebug@software.joehewitt.com)
  • Troubleshooter 1.1a (troubleshooter@mozilla.org)
  • Norton Toolbar 2013.3.5.1 ({2D3F3651-74B9-4795-BDEC-6DA2F431CB62}) (Inactive)
  • Norton Vulnerability Protection - 5 ({BBDA0591-3099-440a-AA10-41764D9DB4DB}) (Inactive)


  • incrementalGCEnabled: True


  • adapterDescription: Intel(R) HD Graphics 4000
  • adapterDescription2:
  • adapterDeviceID: 0x0166
  • adapterDeviceID2:
  • adapterDrivers: igdumd64 igd10umd64 igd10umd64 igdumd32 igd10umd32 igd10umd32
  • adapterDrivers2:
  • adapterRAM: Unknown
  • adapterRAM2:
  • adapterVendorID: 0x8086
  • adapterVendorID2:
  • direct2DEnabled: True
  • directWriteEnabled: True
  • directWriteVersion: 6.2.9200.16433
  • driverDate: 7-20-2012
  • driverDate2:
  • driverVersion:
  • driverVersion2:
  • info: {u'AzureCanvasBackend': u'direct2d', u'AzureFallbackCanvasBackend': u'cairo', u'AzureContentBackend': u'direct2d'}
  • isGPU2Active: False
  • numAcceleratedWindows: 1
  • numTotalWindows: 1
  • webglRenderer: Google Inc. -- ANGLE (Intel(R) HD Graphics 4000)
  • windowLayerManagerType: Direct3D 10

Modified Preferences

  • accessibility.typeaheadfind.flashBar: 0
  • browser.cache.disk.capacity: 358400
  • browser.cache.disk.smart_size.first_run: False
  • browser.cache.disk.smart_size.use_old_max: False
  • browser.cache.disk.smart_size_cached_value: 358400
  • browser.places.smartBookmarksVersion: 4
  • browser.startup.homepage: http://localhost/
  • browser.startup.homepage_override.buildID: 20130511120803
  • browser.startup.homepage_override.mstone: 21.0
  • browser.tabs.loadInBackground: False
  • dom.mozApps.used: True
  • dom.w3c_touch_events.expose: False
  • extensions.lastAppVersion: 21.0
  • font.internaluseonly.changed: True
  • font.name.serif.x-western: Verdana
  • gfx.direct3d.prefer_10_1: True
  • network.cookie.prefsMigrated: True
  • places.database.lastMaintenance: 1369637750
  • places.history.expiration.transient_current_max_pages: 104858
  • plugin.disable_full_page_plugin_for_types: application/pdf
  • privacy.sanitize.migrateFx3Prefs: True


  • User JS: No
  • Accessibility: No
  • Top 10 Contributor
2385 solutions 21079 answers

Helpful Reply

Do you use a port number in your localhost URLs? If so, have you noticed any changes to (or omission of) those numbers as you test the application?

Although I don't think you can do a reload bypassing cache (Ctrl+Shift+r) in the source viewer, if you do that in a page that wasn't able to load the script, does that help?

Question owner

Thanks for yor reply.

No, I don't use a port number in the localhost URL.

Yes a 'reload bypassing cache' (ctrl+shift+r) on the 'warning' window does find the JS source, and the application subsequently runs.

This doesn't explain why Firefox can't find the JS file initially - and will make testing a bit of a minefield.